The durability of synthetic materials used for heart valve leaflets under the repetitive loads of the opening and closing is dependent, in part, on the load distribution between the leaflet and the frame. Further, substantial load is encountered on the leaflet when in the closed position. Mechanical failure of the leaflet can arise, for example, at the mounting edge, where the flexible leaflet is supported by the relatively rigid frame. The repetitive loads of leaflet opening and closing leads to material failure by fatigue, creep or other mechanism, depending in part on the leaflet material. Mechanical failure at the mounting edge is especially prevalent with synthetic leaflets.
The durability of the valve leaflets is also a function of the character of bending by the leaflet during the opening-closing cycle. Small radius bends, creases and intersecting creases, can produce high stress zones in the leaflet. These high stress zones can cause the formation of holes and tears under repetitive loading.
Prosthetic valves may be delivered using surgical or transcatheter techniques. A surgical valve is implanted into a patient using open-heart surgical techniques. The surgical valve is usually manufactured to have a fixed diameter as opposed to a transcatheter valve which is required to attain a range of diameters for access and delivery. The surgical valve is usually provided with a sewing cuff about a perimeter of the valve to allow for suturing to the native tissue orifice.
In addition to the valve durability issues discussed above, the transcatheter valve must also be able to withstand the handling and deployment stresses associated with being compressed and expanded
A “preferred” shape of synthetic heart valve leaflets has been described many times, but each is different from the others. The various transient three dimensional shapes range from spherical or cylindrical to truncated conical intersections with spheres, and an “alpharabola”. The shape most often described as “preferable” is modeled after the native human aortic valve. Though nature dictates the optimum shape for the native tissues to form a heart valve, we have discovered this is not true for synthetic materials.